Transmitting antenna



Jan. 19, 1937.

e. H. BROWN TRANSMITTING ANTENNA Filed July 26, 1935 ru w w. W v

"MM F Patented Jan. 19, 1937 v UNITED STATES PATENT GFFIQE TRANSIVHTTING ANTENNA poration of Delaware Application July 26, 1935, Serial No. 33,281

'7 Claims.

My invention relates broadly to transmitting antennas. More particularly, my invention is an improved transmitting antenna which has an effective height greater than its actual height. Briefly my invention might be termed a sectionalized transmitting antenna.

One of the objects of my invention is to simulate a tall broadcasting antenna with one whose actual height is considerably less.

Another object is to control the relative com.- ponents of vertical and horizontal radiation characteristics of the antenna.

Another object is to control the characteristic of the antenna which governs the relative effective day and night ranges.

A further object is to design an antenna system which will be practical from a structural standpoint.

Further objects will appear in the following description and claims.

It has been Well established that the most efiective height for a straight vertical wire antenna is 230 or approximately 0.639 of a wave length for the maximum horizontal signal along the ground. However, an antenna of this dimension will radiate a substantial sky wave which will limit the effective night range of the transmitter. The sky wave may be suppressed to the optimum degree by shortening the antenna length to 190 or approximately 0.528 of a wave length. It has also been found that a capacity may be arranged at the top of a vertical antenna to reduce the vertical or sky wave radiation component. The effective length may be varied by inserting an inductance between the antenna and the capacity structure located at the top of the antenna. Although these various structures are effective, several limitations reduce their utility.

In the case of vertical antennas the maximum actual height has been limited by governmental regulations for the safety of aircraft. In the use of a. capacity top the physical limitation that the area of the capacity structure must be large in comparison to the supporting tower is a decided handicap. If the supporting structure is tapered to withstand the mechanical stresses, a relatively large area of capacity to the area at the top of the tower may be used, but with a new disadvantage that the tapered tower has a deleterious effect on the form of the radiated wave. The insertion of a loading inductance between the capacity and tower requires careful insulation to withstand the relatively high voltages. I have also determined that the loading inductance between the capacity and tower is less efiicient than the sectional arrangement I employ. Figure 1 is a perspective view showing a schematic outline of one form of my invention,

Figure 2 illustrates schematically a modified form of my invention,

Figure 3 is an elevational view of the inductance coil and shield employed in my device, and

Figure 4 is a diagrammatic illustration of the current distribution in a sectionalized antenna.

In Figure 1 a tower structure of uniform cross section is represented as I. The base of the tower is insulated from earth 3 by suitable insulators 5. The tower is connected by one or more leads I to a transformer 9 which is coupled to a transmitter represented by M. It should be understood that a transmission line (not shown) may couple the antenna tower and the transmitter H.

The height of the tower, by way of example, may be from to 180 or expressed in percentages 33 /3% to 50% of the wave length to be transmitted. Insulators B3 are inserted in the legs of the tower at a point about two-thirds up the tower. This dimension is not critical, and may be from about two-thirds to five-sixths. The tower structure is designed to make all parts of the tower above the insulators electrically free from the lower portion. Just below the insulators, on a platform i5, is mounted an inductance coil II. The value of this inductance may be varied by means of a movable clip it (see Figure 3). A shielding member 2! surrounds the inductance IT. The shield is grounded to the lower tower section. The upper terminal 23 attaches to clip l9 and connects to the inductance. The terminal extends through an insulated bushing 25. The terminal 23 is connected to the upper section of the tower. The clip i9 may beadjusted on the inductance by reaching through an opening or door 21. The value of inductance H is from about 25 microhenries to microhenries.

By adjusting the value of the inductance, I have found that the relative radiation of the horizontal and vertical wave components may be varied to produce maximum range of day or night transmission. The actual factors governing the two types of transmission service are necessarily complicated. For example, the vertical or skywave component of radiation will be reflected from the heaviside layer to a distant point where it joins the horizontal or ground wave components. It is difficult to predict these reflected components. Instead of predicting the factors I find that observation stations may be established at varying distances from the transmitter to receive the transmitted wave. These stations report the result of a series of systematic changes in the inductance H until a maximum effective transmission service is found.

This adjustment must not be confused with the resonance adjustment of an ordinary loading coil and antenna. In Figure 4 the curve 3! represents the usual current distribution in a half Wave length vertical antenna- The current disslow. Instead of adjusting to the maximum in-f dicated by the observations of distant receivers,

I have devised a method and apparatus for making the required inductance adjustment, which is fully described in my copending application, Serial No. 35,919, filed on August 13, 1935, and entitled Apparatus and method for adusting transmitting antennas.

Although I prefer a tower structure of uniform cross section, my invention may be employed in connection with a tapered tower. The tapered tower may have an effect on the radiation characteristics. I prefer to modify a tapered tower as shown in Figure 2. A tower is divided into an upper section 31 and a lower section 39. These sections are insulated from each other by insulators 4|. An adjustable inductance 43, shielded by 45, connects the upper and lower tower sections. On the top of 31are mounted outriggers 41. The length of each outrigger is substantially equal to the diagonal distance between the legs at the base of the tower. Vertical wires 49 are dropped from the ends of the Outriggers. Sup-ports 5| hold the Wires with respect to the base of the upper section 31 of the tower. The upper section 31 and the vertical wires 49 are connected to the inductance 43. A

7 similar set of outriggers 53 are mounted on the top of the lower section 39. Vertical wires 55 connect 53 with the base of the tower above insulators 51. The inductance 43 joins the electrified parts of the upper and lower tower sections. The outriggers and vertical wires give the tapered tower the efiect of a uniform cross section. I prefer this modification in the case of a tapered tower, but it should be understood that my invention may be employed without such change.

I have found that my invention is more adapted to tall vertical antenna tower sections than the capacity top antenna. The inductance at the capacity top is subject to high voltage strains; it does not greatly aid the radiation resistance, and it is diificult to structurally provide sufficient insulation. With my sectionalized tower, the upper section greatly aids the radiation resistance; a smaller inductance may be employed, thereby reducing ohmic resistance losses, and lower voltage strains permit several practical types of insulation structure.

From the foregoing description it will be apparent that various other modifications may be made in my invention without departing from the spirit and scope thereof, and I desire, therefore, that only such limitations shall be imposed thereon as are necessitated by the prior art and set forth in the appended claims. For example, I ordinarily use the tower structure as the conductive sections of the aerial. Instead of this arrangement the aerial structure may be of insulated material such as wood and the conductive sections may be of wire, pipe, or the like, supported by the insulated structure.

I claim:

1. A transmitting antenna comprising vertical sections of a combined height less than one half of the wave length to be transmitted, an insulated section between said sections, an inductance bridging said insulating section and joining the first mentioned sections at substantially two-thirds of the distance from the base to the top of said antenna, and means for adjusting said inductance so that the ratio between the vertical and horizontal radiation from said antenna may be adjusted by varying the current distribution in said sections.

2. A transmitting antenna comprising vertical sections of a length less than one-half the wave length to be transmitted, an insulating section between said sections, the lengths of said vertical sections being proportioned to establish a minimum voltage drop between them and an adjustable inductance connecting the first mentioned sections, so that the relative amounts of vertical and horizontal radiation from said antenna may be varied by adjusting said inductance thereby varying the current distribution in said sections.

3. A transmitting antenna including two vertical sections of unequal lengths and a combined length of less than one-half the wave length to be transmitted, the length of the lower of said vertical sections being approximately twice the length of the upper of said sections, an adjustable inductance connecting said sections, and means for impressing high frequency currents on said sections whereby the high frequency current may be distributed in said sections to vary the relation between vertical and horizontal radiation of said transmitted wave.

4. A device of the character described including a vertical section of antenna, means insulating said vertical section from earth, a second vertical section of less length than the first mentioned section, the lengths of said vertical sections being proportioned to establish a minimum voltage drop between them, means supporting and insulating the second section with respect to the top of the first mentioned section, an inductance coil connecting the first and second mentioned sections, a source of high frequency current, means coupling said source and said antenna sections, and means for effecting the relative distribution of high frequency current in said sections, to efiect the optimum ratio between vertical and horizontal radiation from said device.

5. A device of the character of claim 4 further characterized by vertical sections having a combined height of less than one-half of the wave length to be transmitted.

6. A device of the character described including a lower vertical antenna structure of substantially uniform cross section, an upper vertical antenna structure or" substantially uniform cross section and of the order of half the length of the first mentioned structure, means for joining and insulating said sections, and an adjustable inductance coil connecting the first and second structures at their junction with said insulating and joining means for varying the current distribution in said sections, whereby desired relationship between vertical and horizontal radiation components of a wave transmitted from said antenna structure may be established by adjusting said inductance.

7. In a device of the character described in claim 6, means'for coupling said first antenna structure with a source of high frequency oscillations.

GEORGE HAROLD BROWN. 

